CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Meshing & Mesh Conversion

[snappyHexMesh] Unable to capture very small nozzle while meshing

Register Blogs Community New Posts Updated Threads Search

Like Tree2Likes
  • 1 Post By surajkvs
  • 1 Post By Yann

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 5, 2022, 02:53
Default Unable to capture very small nozzle while meshing
  #1
New Member
 
SURAJ
Join Date: Jun 2017
Location: IIT KANPUR,India
Posts: 15
Rep Power: 8
surajkvs is on a distinguished road
Dear all,

I have a geometry of order 10m and have 12 nozzles (small patches on walls)of diameter 6mm.

When I am performing snappyHexMesh, then nFaces for nozzles is coming "zero". Although I have given very high surfaceRefinement level for nozzles. I am unable to capture it.

Can anybody guide me what should I do to capture nozzles while meshing.
neelcfd likes this.
surajkvs is offline   Reply With Quote

Old   May 5, 2022, 03:33
Default
  #2
Senior Member
 
Yann
Join Date: Apr 2012
Location: France
Posts: 1,066
Rep Power: 26
Yann will become famous soon enough
Hi Suraj,

In order to help you, we would need more information about your case : screenshots of your geometry and mesh, blockMesh cell size, snappyHexMeshDict...

Regards,
Yann
surajkvs likes this.
Yann is offline   Reply With Quote

Old   May 5, 2022, 07:09
Default
  #3
New Member
 
SURAJ
Join Date: Jun 2017
Location: IIT KANPUR,India
Posts: 15
Rep Power: 8
surajkvs is on a distinguished road
Hello Yann,

Thanks for the reply.
I have attached 3 pics. 1st is full geometry. The geometry contains two legs(downLeg and upLeg). The upLeg is shown in pic2. There are 12 small nozzles on upLeg surface. A few are visible from front view as shown in pic3.

Quote:
Quote:
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v2112 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

backgroundMesh
{
xMin -2;
xMax 2;
yMin -5;
yMax 1.8;
zMin -2;
zMax 2;
xCells 100;
yCells 170;
zCells 100;
}

scale 1;

vertices
(
($:backgroundMesh.xMin $:backgroundMesh.yMin $:backgroundMesh.zMin)
($:backgroundMesh.xMax $:backgroundMesh.yMin $:backgroundMesh.zMin)
($:backgroundMesh.xMax $:backgroundMesh.yMax $:backgroundMesh.zMin)
($:backgroundMesh.xMin $:backgroundMesh.yMax $:backgroundMesh.zMin)

($:backgroundMesh.xMin $:backgroundMesh.yMin $:backgroundMesh.zMax)
($:backgroundMesh.xMax $:backgroundMesh.yMin $:backgroundMesh.zMax)
($:backgroundMesh.xMax $:backgroundMesh.yMax $:backgroundMesh.zMax)
($:backgroundMesh.xMin $:backgroundMesh.yMax $:backgroundMesh.zMax)
);

blocks
(
hex (0 1 2 3 4 5 6 7)
(
$:backgroundMesh.xCells
$:backgroundMesh.yCells
$:backgroundMesh.zCells
)
simpleGrading (1 1 1)
);

edges
(
);

boundary
(
);

mergePatchPairs
(
);


// ************************************************** *********************** //

Quote:
Quote:
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v2112 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object snappyHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

// Which of the steps to run
castellatedMesh true;
snap true;
addLayers true;


// Geometry. Definition of all surfaces. All surfaces are of class
// searchableSurface.
// Surfaces are used
// - to specify refinement for any mesh cell intersecting it
// - to specify refinement for any mesh cell inside/outside/near
// - to 'snap' the mesh boundary to the surface
geometry
{
mesh1.stl
{
type triSurfaceMesh;
name RH;
regions
{
laddleWalls {name laddleWalls;}
laddleFS {name laddleFS;}
vaccumBC {name vaccumBC;}
vaccumChambWalls {name vaccumChambWalls;}
//inletDown {name inletDown;}
nozzles {name nozzles;}
upLeg {name upLeg;}
downLeg {name downLeg;}
//snorkelOuterWalls {name snorkelOuterWalls;}






}
}

refinementCyl
{
type searchableCylinder;
point1 (-0.7 0 0);
point2 (-0.7 -1.750 0);
radius 0.3;
//type upLegCyl;
//min (-350 0 -350);
//max ( 8.0 0.7 2.5);
}
}


// Settings for the castellatedMesh generation.
castellatedMeshControls
{

// Refinement parameters
// ~~~~~~~~~~~~~~~~~~~~~

// If local number of cells is >= maxLocalCells on any processor
// switches from from refinement followed by balancing
// (current method) to (weighted) balancing before refinement.
maxLocalCells 10000000;

// Overall cell limit (approximately). Refinement will stop immediately
// upon reaching this number so a refinement level might not complete.
// Note that this is the number of cells before removing the part which
// is not 'visible' from the keepPoint. The final number of cells might
// actually be a lot less.
maxGlobalCells 20000000;

// The surface refinement loop might spend lots of iterations refining just a
// few cells. This setting will cause refinement to stop if <= minimumRefine
// are selected for refinement. Note: it will at least do one iteration
// (unless the number of cells to refine is 0)
minRefinementCells 10;

// Allow a certain level of imbalance during refining
// (since balancing is quite expensive)
// Expressed as fraction of perfect balance (= overall number of cells /
// nProcs). 0=balance always.
maxLoadUnbalance 0.10;


// Number of buffer layers between different levels.
// 1 means normal 2:1 refinement restriction, larger means slower
// refinement.
nCellsBetweenLevels 3;



// Explicit feature edge refinement
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

// Specifies a level for any cell intersected by its edges.
// This is a featureEdgeMesh, read from constant/triSurface for now.
features
(
{
file "mesh1.eMesh";
level 2;
}
);



// Surface based refinement
// ~~~~~~~~~~~~~~~~~~~~~~~~

// Specifies two levels for every surface. The first is the minimum level,
// every cell intersecting a surface gets refined up to the minimum level.
// The second level is the maximum level. Cells that 'see' multiple
// intersections where the intersections make an
// angle > resolveFeatureAngle get refined up to the maximum level.

refinementSurfaces
{
RH
{
level (0 0);

regions
{
nozzles
{
level (8 8);
patchInfo
{
type patch;
}
}
/* inletDown
{
level (5 5);
patchInfo
{
type patch;
}
}
inletUp
{
level (5 5);
patchInfo
{
type patch;
}

} */

vaccumBC
{
level (2 2);
patchInfo
{
type patch;
}

}
laddleFS
{
level (2 2);
patchInfo
{
type patch;
}

}
/*snorkelOuterWalls
{
level (1 1);
patchInfo
{
type wall;
}

} */
vaccumChambWalls
{
level (2 2);
patchInfo
{
type wall;
}

}
laddleWalls
{
level (2 2);
patchInfo
{
type wall;
}

}
downLeg
{
level (2 2);
patchInfo
{
type wall;
}

}
upLeg
{
level (3 3);
patchInfo
{
type wall;
}

}

}
}


}

// Resolve sharp angles
resolveFeatureAngle 90;


// Region-wise refinement
// ~~~~~~~~~~~~~~~~~~~~~~

// Specifies refinement level for cells in relation to a surface. One of
// three modes
// - distance. 'levels' specifies per distance to the surface the
// wanted refinement level. The distances need to be specified in
// descending order.
// - inside. 'levels' is only one entry and only the level is used. All
// cells inside the surface get refined up to the level. The surface
// needs to be closed for this to be possible.
// - outside. Same but cells outside.

refinementRegions
{
refinementCyl
{
mode inside;
levels ((1E15 3));
}
}


// Mesh selection
// ~~~~~~~~~~~~~~

// After refinement patches get added for all refinementSurfaces and
// all cells intersecting the surfaces get put into these patches. The
// section reachable from the locationInMesh is kept.
// NOTE: This point should never be on a face, always inside a cell, even
// after refinement.
locationInMesh (0 0.3 0);


// Whether any faceZones (as specified in the refinementSurfaces)
// are only on the boundary of corresponding cellZones or also allow
// free-standing zone faces. Not used if there are no faceZones.
allowFreeStandingZoneFaces true;
}



// Settings for the snapping.
snapControls
{
//- Number of patch smoothing iterations before finding correspondence
// to surface
nSmoothPatch 3;

//- Relative distance for points to be attracted by surface feature point
// or edge. True distance is this factor times local
// maximum edge length.
tolerance 0.0002;

//- Number of mesh displacement relaxation iterations.
nSolveIter 30;

//- Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 5;

// Feature snapping

//- Number of feature edge snapping iterations.
// Leave out altogether to disable.
nFeatureSnapIter 20;

//- Detect (geometric only) features by sampling the surface
// (default=false).
implicitFeatureSnap false;

//- Use castellatedMeshControls::features (default = true)
explicitFeatureSnap true;

//- Detect points on multiple surfaces (only for explicitFeatureSnap)
multiRegionFeatureSnap false;
}



// Settings for the layer addition.
addLayersControls
{
// Are the thickness parameters below relative to the undistorted
// size of the refined cell outside layer (true) or absolute sizes (false).
relativeSizes true;

// Per final patch (so not geometry!) the layer information
layers
{
wall
{
nSurfaceLayers 3;
}

moldWalls
{
nSurfaceLayers 3;
}

}

// Expansion factor for layer mesh
expansionRatio 1.3;

// Wanted thickness of final added cell layer. If multiple layers
// is the thickness of the layer furthest away from the wall.
// Relative to undistorted size of cell outside layer.
// See relativeSizes parameter.
finalLayerThickness 0.03;

// Minimum thickness of cell layer. If for any reason layer
// cannot be above minThickness do not add layer.
// Relative to undistorted size of cell outside layer.
minThickness 0.006;

// If points get not extruded do nGrow layers of connected faces that are
// also not grown. This helps convergence of the layer addition process
// close to features.
// Note: changed(corrected) w.r.t 1.7.x! (didn't do anything in 1.7.x)
nGrow 0;

// Advanced settings

// When not to extrude surface. 0 is flat surface, 90 is when two faces
// are perpendicular
featureAngle 60;

// At non-patched sides allow mesh to slip if extrusion direction makes
// angle larger than slipFeatureAngle.
slipFeatureAngle 30;

// Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 3;

// Number of smoothing iterations of surface normals
nSmoothSurfaceNormals 1;

// Number of smoothing iterations of interior mesh movement direction
nSmoothNormals 3;

// Smooth layer thickness over surface patches
nSmoothThickness 10;

// Stop layer growth on highly warped cells
maxFaceThicknessRatio 0.5;

// Reduce layer growth where ratio thickness to medial
// distance is large
maxThicknessToMedialRatio 0.3;

// Angle used to pick up medial axis points
// Note: changed(corrected) w.r.t 1.7.x! 90 degrees corresponds to 130
// in 1.7.x.
minMedialAxisAngle 90;


// Create buffer region for new layer terminations
nBufferCellsNoExtrude 0;


// Overall max number of layer addition iterations. The mesher will exit
// if it reaches this number of iterations; possibly with an illegal
// mesh.
nLayerIter 50;
}



// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
#include "meshQualityDict"


// Advanced

//- Number of error distribution iterations
nSmoothScale 4;
//- Amount to scale back displacement at error points
errorReduction 0.75;
}


// Advanced

// Write flags
writeFlags
(
scalarLevels
layerSets
layerFields // write volScalarField for layer coverage
);


// Merge tolerance. Is fraction of overall bounding box of initial mesh.
// Note: the write tolerance needs to be higher than this.
mergeTolerance 1e-6;


// ************************************************** *********************** //
Regards,
Suraj
Attached Images
File Type: png pic1_full_image.PNG (88.7 KB, 22 views)
File Type: png pic2_upLeg.PNG (47.0 KB, 24 views)
File Type: png pic3_nozzles.PNG (37.1 KB, 22 views)
surajkvs is offline   Reply With Quote

Old   May 6, 2022, 02:35
Default
  #4
Member
 
Al Csc
Join Date: Jul 2018
Posts: 30
Rep Power: 7
al.csc is on a distinguished road
Run surfaceFeatureExtract and use that output for snappy. In alternative I would refine that area and use topoSet, to select the corresponding faces and use them as inlet for the nozzles. I guess with that low detail you don t care if the nozzles have a cylindrical or square section, as soon as the mass flux matches.
al.csc is offline   Reply With Quote

Reply

Tags
snappyhexmesh 3d


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
[Commercial meshers] Problems in meshing 2D axisymmetric nozzle wedge with Salome kim4545 OpenFOAM Meshing & Mesh Conversion 1 March 20, 2023 11:05
Nozzle meshing, critical convergence kovage STAR-CCM+ 0 March 28, 2022 04:36
[ICEM] 3D Nozzle meshing saadia ANSYS Meshing & Geometry 0 April 20, 2021 14:50
Meshing a nozzle parvaz747 Mesh Generation & Pre-Processing 3 June 17, 2013 11:40
Small Supersonic Nozzle Paal Main CFD Forum 3 November 25, 2003 04:59


All times are GMT -4. The time now is 11:51.